In fabricating integrated circuits (IC's) on a surface of a semiconductor wafer, a number of electronic devices are formed on or within the surface of the wafer. Any of a number of electronic devices may be formed on the surface of the wafer, such as transistors, capacitors, diodes, etc. Electronic devices include active areas such as a body region of a transistor, or a source/drain region of a transistor.
After the individual electronic devices are formed on the surface of the wafer, selected electronic devices must be interconnected to form the IC. One typical approach to interconnecting electronic devices is to deposit metal interconnect traces on the surface of the wafer, usually on top of the electronic devices. The interconnect traces typically take the form of trace lines, with a line width that is generally consistent along a length of the trace line. The traces connect at least one active region of a first electronic device with an active region of a second electronic device, allowing the devices to communicate with one another, and perform complex operations such as processing or storing information.
Trace lines, however, create a rough surface on the wafer with the trace lines as high points, and the spaces between traces as low points. In many IC designs, there is a need to form a substantially planar surface on the wafer over the trace lines. For example, most IC designs stack multiple layers of electronic devices on top of each other. Layers of trace lines interconnect electronic devices on each respective layer, frequently with vias connecting between layers. The surface of each trace line layer must be substantially planar, and electrically isolated in order to form subsequent layers of electronic devices.
One approach in the industry has been to deposit an inter layer dielectric (ILD) over the trace lines. The ILD electrically isolates the trace line layer, and it can be planarized to form the necessary surface for subsequent layers. Current devices and methods design a pattern of trace lines that merely considers electrical connection of electronic devices. The effects of the chosen pattern on subsequent wafer fabrication steps such as deposition of an ILD layer is not currently considered. Current devices and methods require multiple steps and multiple layers for effective isolation and planarization of the trace line layer. Current devices and methods also produce significant variation in ILD thickness. Current devices and methods are thus more costly due to additional fabrication steps, and less reliable due to resulting thickness variations. Thick ILD layer regions are undesirable, because formation of subsequent vias is difficult due to the extra distance that the vias must tunnel through. Variation in ILD thickness is undesirable because, among other problems, subsequent via etching must either under etch thick regions, or over etch thin regions of the ILD.
As discussed in commonly assigned, co-pending applications, the design of the pattern of elements can influence the effectiveness of subsequent operations such as deposition of ILD layers. Computer programs exist that are used to generate patterns of elements such as trace lines, and can be used to modify planned patterns of elements. The computer programs typically generate a pattern for a chip or an entire die using combinations of smaller pattern organization devices called cells. A cell can contain shapes or instances, or both shapes and instances. A shape is defined as a collection of data that defines geometry of a structure such as a trace line. An instance is defined as data indicating a placement of another cell within the current cell, but not including the actual shape geometry data. Cells are arranged in a hierarchy that includes low level cells, intermediate level cell, high level cells, etc. High level cells typically include large numbers of lower level cells, and the relationship of lower level cells within high level cells is frequently complicated. The use of cells arranged in a hierarchy is convenient for designing and making modifications to a pattern of elements, because repeating modifications can be made at the appropriate level within the hierarchy, and the changes will be repeated throughout similar level cells. Recognizing and utilizing repeating patterns reduces processing time for a computer or similar data processor during the design and modification process.
A problem arises, however, when performance of a selected cell in a selected level within the hierarchy is influenced by factors external to the selected cell, such as factors from a separate adjacent cell. Without knowledge of the characteristics of cells external to a selected cell or cells, modifications can fail to accomplish the design goals of the modification, or the modification can introduce new problems in the pattern of elements.
What is needed is a method of design and modification for patterns of elements that allows consideration of a region within the pattern that is inclusive enough to encompass substantially all relevant features so that they can be considered in design and modification. What is also needed is a method of design and modification with a short processing time.